Phototitrimetric determination of sulfhydryl compounds witho-hydroxymercuribenzoic acid using dithiofluorescein as an indicator

Summary A phototitrimetric method for the determination of sulfhydryl compounds in an aqueous medium is described.o-Hydroxymercuribenzoic acid is used as a titrant with dithiofluorescein as an indicator. Disulfide amino acids like cystine and-substituted DL-cystines are reduced with sodium borohydride before titration. All amino acids were determined to the limit of 1.0mol with an error of less than 4%. A selective phototitrimetric method for the determination of-mercaptopyruvate in presence of cysteine and glutathione is described. This method can be extended to the microdetermination of other similar sulfhydryl compounds in biological materials.

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Zusammenfassung Eine phototitrimetrische Bestimmungsmethode für Sulfhydrylverbindungen in wäßriger Phase wurde beschrieben. Als Maßflüssigkeit diento-Hydroxymercuribenzoesäure, als Indikator Dithiofluorescein. Aminosäuredisulfide wie Cystin und-substituierte DL-Cystine werden vor der Titration mit Natriumborhydrid reduziert. Alle Aminosäuren lassen sich bis zur Größenordnung von 1,0Mol mit einem Fehler von weniger als 4% bestimmen. Eine selektive phototitrimetrische Bestimmung von-Merkaptopyruvat in Gegenwart von Cystein und Glutathion wurde angegeben. Das Verfahren läßt sich auch für andere Sulfhydrylverbindungen in biologischem Material anwenden.

     

Molecular structures,vibrational assignments and barriers to pseudorotation of gaseous niobium pentachloride and tantalum pentachloride from electron diffraction data

The pentachlorides of niobium and tantalum have trigonal bipyramidal structures (D_3hsymmetry) with thermal average axial bonds, r_α, longer than the equatorial ones by 0.097(9) and 0.142(5) Å, respectively. The equatorial bonds are r(Nb—Cl) = 2.241(4) and r(Ta—Cl) = 2.227(3) Å. Standard deviations are given. Calculated amplitudes of vibration for the e' type of bending frequencies assigned as v₆ (equatorial in-plane bend) < v₇ (axial—equatorial bend) agree significantly better with the experimental vibrational amplitudes than do amplitudes computed for the opposite assignment. Assuming an analytical quartic-harmonic potential for the pseudorotational motion of the molecules, barriers to pseudorotation of 1.5(0.7) and 1.2(0.6) kcal mol^?1 are estimated from the electron diffraction data for NbCl₅ and TaCl₅, respectively. Effects from interatomic multiple scattering are included in the theoretical intensities, and are found to be of some importance to the results.     

Research on a number of substituted arylamides of dithiocarboxylic acids

Dithiomalonic acid diarylamldes are cyclized to 3,5-diarylamino-1,2-dithiolium halides by oxidation with an equivalent amount of bromine (iodine) in chloroform solution; the same amides are cyclized to 4-bromo-3,5-diarylamino-1,2-dithiolium bromides with excess bromine and to 3-arylamino-5-arylimino-1,2-dithiols in alkaline media with potassium ferricyanide. The behavior of the synthesized substituted 1,2-dithiols with respect to various reagents was studied.     

Infrared studies of chromones—II Isotopically substituted 5-hydroxychromones

By deuteration of the OH group, it has been shown that two bands, at 1665 and 1630 cm⁻¹ (CCl₄), in the IR spectra of 5-hydroxychromones are associated with the H-bonded CO stretching vibration. Nuclear deuteration of 5-hydroxy-2-methylchromone (1) under acidic conditions gave a tri- and a hexadeutero derivative; the latter, isotopically substituted at C-3, shows a single CO band at 1649 cm⁻¹. Hydrolysis of 3-acetyl-5-hydroxy-2-methylchromone with sodium carbonate in deuterium oxide furnished 5-hydroxy-2-trideuteromethylchromone-3-d which also exhibits a single CO absorption. Partial incorporation of O¹⁸ into the CO group of 1 results in a single ν_C=O¹⁸ at 1593 cm⁻¹. It is suggested that the doublet CO absorption of 5-hydroxychromones arises from a Fermi resonance involving a low-energy vibrational mode of the vinyl proton on the nuclear C-3 position.     

Energetic calculations of the chain conformation of isotactic polymers of olefins in the crystalline state

Energetic calculations have been carried out on a correlated series of isotactic aliphatic polymers (polypropylene (PP), poly-α-butene (PB), poly-3-methylbutene (P3MB), poly-(S)-3-methylpentene-1 (P(S)3MP) and isotactic polystyrene (PS). The possible variation of the CCC bond angles and of all the internal rotation angles (no group of atoms being taken as a unit) was considered.The possibility to predict the experimental helical parameters without any previous assumption is discussed. The differences in the shape of the minima for polymers with aliphatic and aromatic branched chains have been critically evaluated.For the P(S)3MP the results have shown how the asymmetric configuration of the side group influences the chain conformation of the polymer.     

Etude semiempirique de la configuration moléculaire stable des molécules ionisées ou excitées

Résumé Les déformations stabilisatrices des molécules ionisées ou excitées sont étudiées en supposant connues les coordonnées normales et les constantes de force de l'état fondamental et en calculant les variations de l'énergie d'ionisation ou d'excitation dans les déformations. On en déduit les coordonnées des minimas, les énergies de stabilisation, et les intersections des surfaces potentielles. Cette méthode est appliquée aux anions de la pyrazine calculés par les méthodes SCF et UHF dans les approximations de Pariser et Parr: les variations des longueurs de liaison sont de l'ordre de 0.15 å, celle de l'affinité électronique de 1 eV, et celle des densités de spin de 0.05 e. Ce phénomène peut jouer un rÔle dans l'eifet de charge. En méthode de Hückel des formules générales sont déduites, donnant l'énergie de stabilisation par déformation des ions et des états excités des polyènes.

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The stabilizing deformations of ionized or excited molecules are studied using experimental normal modes and force-constants, and calculating the variations of ionization or excitation energies in the deformations. We deduce new minimas, stabilizing deformations, crossing lines of potential surfaces. This method is applied to negative ions of pyrazine by SCF and UHF (Unstricted Hartree-Fock) methods in the Pariser-Parr approximations: the variations of bond lengths could reach 0.15 å, the electroaffinity could increase of 1 eV, and the spin densities change about 0.05 e. This phenomenon may play a role on the so-called charge-effect. In that scheme, general formulas giving the stabilizing deformation energies for ions and excited states of polyens are deduced from Hückel method.

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Zusammenfassung Die stabilisierenden Deformationen ionisierter oder angeregter Moleküle werden bei bekannten Normalkoordinaten und Kraftkonstanten des Grundzustandes studiert und die Änderungen der Ionisations- und Anregungsenergie bei den Deformationen berechnet. Hieraus werden die Minimumskoordinaten, Stabilisierungsenergien und Schnitte der PotentialflÄchen hergeleitet. Diese Methode wird auf die Anionen von Pyrazin mittels der SCF- und UHF-Methode im Rahmen der Pariser-Parr-NÄherung angewandt. Die Änderungen der BindungslÄngen betragen grö\enordnungsmÄ\ig 0,15 å, die der ElektronenaffinitÄten 1 eV und die der Spindichten 0,05 e. Dieses PhÄnomen spieltbeim sogenannten Ladungseffekt eine Rolle. Mit der Hückel-Methode werden allgemeine Formeln abgeleitet, die die Stabilisierungsenergie der Deformation der Ionen und angeregten ZustÄnde von Polyenen angeben.

     

4-carboxy-1,2-cyclohexanedionedioxime complexes of nickel(ii) in alkaline media

The reactions of 4-carboxy-1,2-cyclohexanedionedioxime and nickel(II) were studied in alkaline media. Spectrophotometric studies indicate the presence of a 1:1 complex ion, NiD^-. Magnetic susceptibility measurements on a series of solutions of varying ratios of vic-dioxime and nickel(II) showed that the 1:1 complex ion was diamagnetic and that two paramagnetic complexes, probably NiD₂^4- and NiD₃^7-, are present in solution. The stability constants for the three complexes were calculated from spectrophotometric and magnetic susceptibility data. The log K values were found to be log K₁ = 28.74 ± 0.60, log K₂ = 0.76 ± 0.15, and log K₃ = 3.67 ± 0.73, respectively.     

On the symmetry of iron(III) tris-acetylacetonate crystals

The crystal structure of iron tris-acetylacetonate is re-determined. Crystal data at 293 K are: a = 15.4524(5) Å, b = 13.5876(4) Å, c = 16.5729(7) Å, Z = 8; at 150 K: a = 15.2541(4) Å, b = 13.4451(3) Å, c = 16.4256(5) Å, Z = 8. The structure is molecular and comprises isolated molecules. The coordination polyhderon of iron is an almost regular octahedron, Fe-O bond lengths are 1.977–2.003 Å (293 K) and 1.982–2.006 Å (150 K). In the crystalline state, the molecules are arranged in layers, and iron atoms are located on a plane yielding an almost regular trigonal net with the Fe...Fe separations of 7.558–8.103 Å (293 K) and 7.472–8.017 Å (150 K). The adjacent layer is positioned exactly over the first one with a Fe...Fe distance of 8.303 Å (293 K) and 8.236 Å (150 K).     

A novel regiodivergent resolution reaction mediated by a homochiral lithium amide base

The reaction of a racemic perhydroisoquinolene derivative 9 with the homochiral lithium amide basse 3 in the presence of Me₃SiCl in an regiodivergent fashion to give the two non-racemic regioisomeric enol silanes 10 and 11. Conversion of 10 into enone 15, an intermediate useful in the synthesis of the alkaloid (+)-yohimbine, was also possible.     

Synthesis and structure of pyrazolo[5,1-a]isoindol-8-ones from Aromatic Ortho Diesters

The title compounds 2 , have now been shown to arise in certain cases from condensation of aromatic ortho-diesters with ketone, where formerly only indeno[1,2-c]pyrazol-4(1H)-ones 3 have been reported from such reaction. Heretofore 2 was obtained in a less direct fashion from phthalaldehydic acid esters. When hetero-aromatic diesters were employed, new heterocyclic ring systems as represented by 2a,b ,c were prepared for the first time. Structures of 2 have been verified from detailed ¹H and ¹³C nmr studies, while representative intermediates 4–9 in the condensation of diesters to 2 have been isolated and identified.